In the satellite communications and telemetry field, it is desirable to have tracking antennas that are inexpensive to construct and that are virtually maintenance free. To permit changes in its orientation, an antenna reflector must be able to pivot about one or more axes, depending on the type of mounting used.
One type of mounting structure is the elevation-over-azimuth type in which structures must provide for independent rotation about the vertical or elevation axis and also about the horizontal or azimuth axis. Previous structures have utilized different drive assemblies to provide the rotational power to achieve the proper elevation and azimuth orientations. A different drive assembly for each orientation is more expensive to design, manufacture and maintain. There exists a need for a modular drive assembly that can be used for either the elevation or azimuth orientation. Typical drive assemblies used in antenna pedestals have a base plate, a bull gear, a ball bearing, a bearing retainer, a motor, and a turntable to allow the reflector and housing to freely rotate.
In designing drive assemblies, it is desirable to use lightweight, inexpensive material so as to reduce the cost and weight of the entire unit. Previous drive assemblies were designed with most of the parts being made from the same material, generally steel or stainless steel. However, stainless steel is expensive and heavy. Conversely, aluminum is fairly inexpensive and lightweight, but has a high coefficient of thermal expansion. When using aluminum and steel parts in the same drive, difficulties arise when the unit is exposed to extremely low temperatures due to the difference between the coefficients of thermal expansion in aluminum and steel. For example, if steel was used as the bearing material and the remaining parts were aluminum, at low temperatures the aluminum would contract much more than the steel and cause considerable radial pressure on the steel bearing. This pressure would inhibit the free rotation of the bearing and thus, the turntable, requiring more output work from the motor to overcome the radial pressure. Thus, there exists a need for a lightweight, less expensive improved drive assembly specifically designed to accommodate thermal expansion and contraction while allowing the bearing to freely rotate.